|Chorus Crank on Shimano BB?||JAM66|
Apr 14, 2003 7:58 AM
|I was told by a local "mechanic" that you could use a Campy Chorus Crank on a Shimano Bottom bracket. So I put the UN-72 BB in and snugged down the Crank Bolts. I know from a Purist pespective that this isn't correct but I couldn't see buying another BB when I had this one laying around. If this is wrong then what are the potential problems?|
|Yes, it's wrong from a technical perspective also...||TJeanloz|
Apr 14, 2003 8:41 AM
|The problem is that although the taper is the same, they start with different sized spindles at the end. The result is that the crank will end up jammed onto the spindle -- not really friction-fit as intended. The chainline will also be off, but if you can get it to shift correctly, this isn't a huge deal. As of now, the damage is done, and you just need to make sure that the crank stays put. Removing the crank is not advisable, as both the crank and BB are likely damaged to the point that they cannot be installed again.|
Apr 14, 2003 8:45 AM
|Although the taper angles are the same, the Shimano spindle is larger than a campy spindle. The crank won't go far enough onto the spindle. The shortest shimano spindle is 103mm and the campy chorus is 102mm. You crank will be located several millimeters too far to the right.
I'll try to find the specs and calculate the error.
Apr 14, 2003 8:57 PM
|I seem to remember this issue from a while back and you may want to search on it, but the pitch of the Campy spindle is not the same as the Shimano spindle. The two shouldn't be mixed. Pitch is the wrong word.... but the amount the crank goes onto the spindle is different for JIS and Euro spindles.
Here's a cut and paste I found on Sheldon Brown's site, but it was taken from somewhere else.
Traditional cotterless cranksets use a tapered square axle end. The sides of the end taper at a 2 degree angle compared to the centerline, 4 degrees compared to each other.
While there is general agreement about the angle, there is no such agreement about the actual width cut off.
ISO vs J.I.S. Standard
Martin Trautmann posted on rec.bicycles.tech:
L_right = 18 +0.5/-0 mm
L_left = 16 +0.5/-0 mm
Dimension across flat 1.5mm from end: 12.6mm +0.02-0.05
Spindle end to bolt seat: Loose: 3mm
Tightened: 1.5mm min.
Yet another source claimed that the squares of Campa, Mavic and
Stronglight (ISO) are smaller than Shimano and Suntour (JIS) with the
result that JIS cranks will move about 4.5 mm further in.
This may conflict with the end of the square and result in a loose fit
or braking stress. for ISO cranks on JIS squares there's less contact
area between crank and spindle, since the crank does not slip perfectly
on the spindle. The result again is a higher risk of braking the crank.
But assuming those 4.5 mm and 2 deg, ISO is about 0.3 mm smaller than
JIS (2 * sin 2 * 4.5 = 0.3)?
ISO cranks (Campagnolo, Stronglight, others) won't go as far onto J.I.S. spindles as they ideally should. J.I.S. cranks (most Japanese models) may bottom out if installed on ISO spindles. In practice, you can very often get away with mixing these sizes, as long as you select an axle length that gives the desired chainline."
I think this is what you need....